The present invention relates to medical sensors for detecting physiological functions and, in particular, to an apparatus for securing an oximeter probe to an appendage of a patient.
Pulse oximetry is a non-invasive medical technique useful for measuring certain vascular conditions. A pulse oximetry system comprises a sensor appliance containing a light source, such as an L.E.D., and a light sensor, such as a photodetector, and is mounted to the finger, toe or earlobe of a patient. The oximetry sensor emits light, which is scattered through a portion of the patient""s tissue where blood perfuses the tissue and the light sensor photoelectrically senses the absorption of light in such tissue. The measurement of light absorbed is used to evaluate various characteristics of a patient such as oxygen saturation of hemoglobin in arterial blood, the volume of individual blood pulsations supplying the tissue, and the rate of blood pulsations corresponding to each heartbeat of a patient.
One kind of commonly used oximetry probe 110 is illustrated in FIGS. 1 and 2. The probe 110 comprises first and second outer shells 112, 114, a spring hinge 116 at the distal end of the probe 110, first and second extending tabs 118, 120, first and second inner pads 122, 124, and a cord 128 connected to the proximal end of the probe. FIG. 1 depicts the oximeter probe 110 in use. The first and second outer shells 112, 114 are separated by forcing the first and second extending tabs 118, 120 toward one another. The patient""s finger or other appendage is then slipped between the first and second inner pads 122, 124. On the exposed faces of the first and second inner pads 122, 124 are the photoemitter and photodetector used to measure various vascular conditions of the patient. The data from the photodetector is then transmitted to an attached console electrical cord 128.
The spring hinge 116 is soft because excessive pressure on the finger can distort pulsations in the finger""s blood supply. As a result, oximetry sensors frequently fall off the patient""s finger when the patient is allowed to move unrestrained.
To prevent excessive movement of a finger to which the probe 110 is attached, medical personnel may secure the hand or arm to the patient""s bed or a stationary object located nearby. A patient would be allowed to move the arm and hand more freely so that discomfort to the patient is avoided. To allow for the patient to move freely while not compromising the security of the oximeter probe 110 upon the finger, an additional means of securing the probe 110 to the patient is necessary.
Further, even small movements by the patient can cause differential motion between the oximeter probe 110 and the patient because the physical construction of the sensors renders them bulky and difficult to securely fasten to a patient""s appendage. Such differential motion causes the signal received by the light sensor to be distorted, resulting in inaccurate measurements of the amount of blood constituent being evaluated.
In practice, reusable oximeter probes are frequently secured to the patient""s appendage using adhesive tape. This method requires that the adhesive tape be applied such that sufficient pressure is applied to the patient""s finger to securely fasten the oximeter probe 110, but not so much that vasoconstriction occurs. If the practitioner creates too much or too little pressure during the initial application of the adhesive tape, it becomes necessary to remove the adhesive tape from the body of the oximeter probe 110 and replace it in a different position. Such readjustment is made difficult by the bond between the tape and the shell of the oximeter probe 110. In addition, the residual adhesive remaining on the shell increases risk of contamination. Further, if the tape is in contact with both the patient""s skin and the oximeter probe 110, removal of the adhesive tape from the patient""s skin can cause irritation, especially when the patient""s skin is particularly sensitive due to trauma or age.
Often, when adhesive tape is used to secure an oximeter probe to the appendage of the patient, the adhesive tape stresses the structure of the oximeter probe. Such distortion occurs if the adhesive tape is not applied with substantially equal pressure on both side openings of the oximeter probe. The undue stress on the spring mechanism that results from such distortion shortens the useful life span of the oximeter probe. Additionally, use of adhesive tape to secure the oximeter probe to the patient also decreases the useful life span of the oximeter probe by making sterilization of the oximeter probe after each use difficult because of adhesive build up. When adhesive tape is removed from the oximeter probe, residue of the adhesive remains on the shell of the probe. Removing the residue may require vigorous scrubbing and/or use of abrasive cleaning agents.
Another concern when securing an oximeter probe to a patient is ensuring that ambient light does not interfere with the signal being received by the photodetector. Outside light is easily scattered and transmitted within the tissue toward the photodetector because skin tissue is translucent. This ambient light causes interference with the signal detected at the photodetector.
Further, vasoconstriction may also be caused by exposure of the appendage to the often cool outside air. Low temperature induced vasoconstriction and the resultant decrease in blood supply may significantly affect the performance of the oximeter probe. Conventional attempts to alleviate the problem of low temperature vasoconstriction include using an integral heater with the sensor and periodic massaging. Heaters, however, must be well regulated to avoid overheating. Furthermore, they increase the complexity of the sensor and can be costly. Periodic massaging can be effective, but usually requires removal of the probe while the appendage is massaged. After some massaging of the appendage to stimulate blood flow to it, the probe is reapplied and measurement resumed. It would be desirable to employ a less complex, passive means for retaining body heat that does not interrupt the measurement process.
The present invention is preferably a strap for securing an oximeter probe to an appendage of a patient. The strap is preferably made of elastic material and may be removably secured to the outside of an oximeter probe to allow for readjustment of the strap after initial application without producing excessive stress on the spring hinge of the oximeter probe.
In one embodiment, the strap is preferably a patch of material comprising a body, a tab located at a proximal end of the body and connected to the body of the strap by a narrow neck, an attachment mechanism for securing the body of the strap about an oximeter probe, and another attachment mechanism for securing the tab about the cord of an oximeter probe. Preferably, at a distal end of the body of the strap is a flap which has a slit through which the extending flap of the top shell of the oximeter probe may be placed to prevent excessive longitudinal movement of the strap.
In another embodiment of the present invention, the strap is preferably a patch of material comprising a body, a tab located at a proximal end of the body and connected to the body of the strap by a narrow neck, one attachment mechanism for securing the body of the strap, a second attachment mechanism for securing the tab and a third attachment mechanism preferably substantially perpendicular to the first and second attachment mechanisms for preventing excessive longitudinal movement of the strap.
In yet another embodiment of the strap, the strap preferably comprises two flaps connected by a neck, one of the flaps having a tab. The strap is secured to the oximeter probe by placing the flaps on opposing sides of the oximeter probe and placing the neck along the spring hinge at the distal end of the oximeter probe. An attachment mechanism is wrapped around the strap enclosing the body of the oximeter probe to secure the probe to an appendage of a patient while a second attachment mechanism is wrapped around the tab of the strap enclosing the cord neck of the oximeter probe to prevent excessive longitudinal movement of the strap.
In yet another embodiment of the present invention the strap is preferably conformed as a sock which, in use, is slipped over the oximeter probe. The strap further comprises two attachment mechanisms. One attachment mechanism is wrapped around the strap about the body of the oximeter probe so that the spring hinge is appropriately compressed on the appendage of the patient. The other is wrapped around the strap enclosing the cord neck of the oximeter probe.
For a fuller understanding of the nature of the present invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.